More than a half-million women in developing countries die each year during childbirth. But a study shows an inexpensive drug could prevent a leading cause of those deaths. The conclusion is based on a study of 10,000 pregnant women. Up to eight percent of pregnant women around the world develop a condition called pre-eclampsia which is marked by high blood pressure and protein in the urine.

Pre-eclampsia can quickly progress to a severe condition known as eclampsia, characterized by convulsions. Untreated, eclampsia can result in maternal death. Researchers estimate 50,000 women in mostly poor countries die of eclampsia each year.

No one knows what causes pre-eclampsia but the risk factors include women with high blood pressure, a first pregnancy and age, either women who are very young or those who are older at the time of conception.

Magnesium sulphate is a very inexpensive drug that's widely dispensed in the United States to women with pre-eclampsia.

"It's been around for a long time, it's not a new drug at all. It's been widely used within the United States for many, many decades. And there has been a lot of debate about whether that's correct or not."

Lelia Duley of Britain's Institute for Health Science in Oxford and a team of international researchers wanted to put the matter to rest once and for all. They conducted a very large trial called the Magnesium Sulphate for Prevention of Eclampsia or Magpie study of 10,000 pregnant women with pre-eclampsia on four continents.

To see whether magnesium sulphate stopped the progression to eclampsia, Dr. Duley says hospitalized women in 33 countries with pre-eclampsia received injections of the drug. Investigators compared the results to women who did not receive the treatment.

"Their effect was a 58 percent reduction, so more than halving of the risk of eclampsia," she said. "And the data also suggest that it is likely that the risk of the women dying was also reduced, although that result was not clearly significant but it certainly looked like it was a trend in that direction."

An oversight committee ended the Magpie trial early, convinced there was enough evidence that magnesium sulphate significantly reduces the risk of eclampsia.

The results of the study were published in the journal The Lancet. Dr. Duley is quick to point out that magnesium sulphate must be given by injection in the hospital. She says women cannot treat themselves by taking a pill.

The burden of pregnancy-related illness and death is in Africa, where nearly 5,000 study participants were recruited. Jack Moodly is with a hospital in Durban that coordinated the study in South Africa among seven centers.

Dr. Moodly says the challenge now is getting enough magnesium sulfate to countries where it is needed. "The major reason for this is the drug is extremely cheap, and if you get multi-national companies they will not produce it," he said.

At five dollars per dose for magnesium sulphate, Dr. Moodly believes pharmaceutical companies must be persuaded to produce the drug and export it to other countries.

He's hoping the World Health Organization will press drug companies to make magnesium sulphate, so this cheap drug might save the lives of thousands of women each year.